The present invention relates to ultrasonic ophthalmic surgical equipment and, in particular, to phacoemulsification, ultrasonic irrigating sleeves and related ultrasonic cutting tips. Ultrasonic irrigating sleeves and ultrasonic cutting tips are critical and principal parts of ultrasonic ophthalmic surgical equipment.
A typical ultrasonic surgical device suitable for ophthalmic procedures consists of an ultrasonically driven handpiece with attached cutting tip and irrigating sleeve and an electronic control console. The handpiece assembly or probe is attached to the control console by an electric cable and flexible tubings. Through the electric cable, the console varies the power level transmitted by the handpiece to the attached cutting tip and the flexible tubings supply irrigation fluid to and draw aspiration fluid from the eye through the handpiece assembly.
The operative part of the handpiece is a centrally located, hollow resonating bar or horn directly attached to a set of piezoelectric crystals. The crystals supply the required ultrasonic vibration needed to drive both the horn and the attached cutting tip during phacoemulsification and are controlled by the console. The crystal/horn assembly is suspended within the hollow body or shell of the handpiece by flexible mountings. The handpiece body terminates in a reduced-diameter portion or nosecone at the body's distal end. The nosecone is externally threaded to accept the irrigation sleeve. Likewise, the horn bore is internally threaded at its distal end to receive the cutting tip. The irrigation sleeve also has an internally threaded bore that is screwed onto the external threads of the nosecone. The cutting tip is adjusted so that the tip projects only a predetermined amount past the open end of the irrigating sleeve. Ultrasonic irrigating sleeves are more fully described in U.S. Pat. Nos. 4,787,889 and 4,808,154, the entire contents of which are incorporated herein by reference.
In use, the ends of the cutting tip and irrigating sleeve are inserted into a small incision of predetermined width in the cornea, or other location. The cutting tip is ultrasonically vibrated within the irrigating sleeve by the crystal-driven ultrasonic horn, thereby emulsifying the selected tissue in situ. The hollow bore of the cutting tip communicates with the bore in the horn that in turn communicates with the aspiration line from the handpiece to the console. A reduced pressure or vacuum source in the console draws or aspirates the emulsified tissue from the eye through the open end of the cutting tip, the cutting tip and horn bores and the aspiration line and into a collection device on the console. The aspiration of emulsified tissue is aided by a saline flushing solution or irrigant that is injected into the surgical site through the small annular gap between the inside surface of the irrigating sleeve and the cutting tip and by the ports at the distal end of the sleeve.
One concern in phacoemulsification surgical procedures is the problem of heat build-up in the cutting tip. Wound pressure on the irrigating sleeve walls compresses the walls and causes both reduced fluid flow to and from the cutting tip and heat-producing frictional contact between the vibrating cutting tip and the walls of the sleeve. Thus, as cooling fluid flow is diminished, frictional heat increases without a means to dissipate the heat. The heat build-up is sudden and pronounced, and can cause scleral or corneal burns very quickly. This problem becomes increasingly a concern when higher frequency (i.e. higher energy) vibrations are used. Prior art handpiece assemblies (or probes) generally have relied on the flow of the irrigant between the cutting tip and the sleeve and the flow of aspirated material into the cutting tip bore to cool the cutting tip. However, the viscoelastic material injected into the anterior ocular chamber during a typical phacoemulsification procedure resists the flow of the irrigant out of the sleeve and is highly resistant to aspiration flow into the cutting tip bore. Therefore, the flow of aspiration and irrigation fluids into and out of the eye can be momentarily occluded whenever the cutting tip and sleeve contact the viscoelastic material. This momentary occlusion can result in sudden cutting tip overheating and resultant scleral and/or corneal lesions because cutting tip overheating occurs very rapidly (within 1 to 3 seconds) and even short term exposure to such overheating can cause injury to delicate eye tissue.
Prior art sleeves have used a variety of techniques to reduce cutting tip heating. For example, in their U.S. Pat. No. 4,787,889, Steppe, et al. disclose a cutting tip cap and sleeve having a smooth bore. The sleeve disclosed by Steppe, et al. reduces the likelihood of cutting tip overheating because the sleeve is fabricated from a rigid resilient resin that resists collapse or compression due to wound pressure.
In his U.S. Pat. No. 4,808,154, Freeman discloses an aspiration and irrigation sleeve with longitudinal ribs along the sleeve bore. The ribs allow the irrigant to flow more readily out the sleeve even under the restrictive effect of wound pressure on the sleeve wall, thereby enhancing the cooling of the cutting tip. However, the sleeve disclosed by Freeman still relies principally on an unoccluded flow of fluids within the cutting tip and sleeve to cool the cutting tip and does not recognize the need to reduce the amount of friction and the resultant heat build-up in the cutting tip.